1. Field of the Invention
The present invention relates to an ink jet type printer head and more particularly to an improvement to implement firm fixation of piezoelectric elements and a vibrating plate in the ink jet type printer head in which ink is jetted from a nozzle and the ink is fed from an ink pool by stacking the piezoelectric elements on a pressure chamber plate on which a plurality of pressure chambers each communicating with the nozzle and the ink pool is formed by boring holes and by individually changing a volume of each of the pressure chambers.
The present application claims priority of Japanese Patent Application No.2000-191190 filed on Jun. 26, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
In recent years, attention is focusing on non-impact type printers because they can be operated at a low noise level during printing and because they can provide high speed printing. Among them, an ink jet type printer in particular attracts interest of users, which performs printing of characters, graphics, photographs or a like by jetting ink drops in a liquid state from a printer head to cause the ink drops to adhere to printing paper and which enables high speed printing and printing on ordinary paper, without special fixing processing. Thanks to these advantages, a variety of ink jet type printers are proposed and put into commercial production.
FIG. 6 to FIG. 10c show operations in a conventional ink jet type printer head in which jetting of ink and replenishing with ink are achieved by changing a volume of a pressure chamber using expansion/contraction deformation effects (uni-morph mode) of piezoelectric elements.
FIG. 6 is a conceptual diagram showing assembly of the conventional ink jet type printer head. The conventional ink jet type printer head is configured by stacking and bonding a nozzle plate 100 having a nozzle 101 for jetting ink, an ink pool plate 200 in which an ink pool (reservoir) 201 is formed, an ink feeding plate 300 in which ink feeding ports 301 are formed, a pressure chamber plate 400 in which a pressure chamber 401 is formed as through holes, a vibrating plate 500 and piezoelectric elements 600. An ink communicating section 700 is used to communicate the nozzle 101 with the pressure chamber 401. The ink communicating section 700 is provided commonly to the ink pool plate 200 and the ink feeding plate 300. An ink sucking port 800 used to feed ink from an ink tank (not shown) to the ink pool 201 is formed in a manner that it penetrates the ink feeding plate 300, the pressure chamber plate 400, and the vibrating plate 500.
Ordinarily, the piezoelectric elements 600 are bonded in advance with the vibrating plate 500. When these components are assembled, by using an alignment hole 900, as a reference, formed in each of the plates, the vibrating plate 500, pressure chamber plate 400, ink feeding plate 300, ink pool plate 200, and nozzle plate 100 are individually or collectively positioned and bonded to each other. An internal structure of the ink jet type printer head formed by the bonding/assembling work is partially taken and shown as a cross-sectional perspective in FIG. 7.
Next, operations of the expansion/contraction deformation in the piezoelectric element 600 and the vibrating plate 500 will be described by referring to FIGS. 7, 8, and 9.
As shown in FIG. 8, at a place corresponding to a position of each of pressure chambers 401, 401, . . . on the pressure chamber plate 400 existing on the vibrating plate 500 is stacked each of the piezoelectric elements 600 in a bonded manner. On a face and back of each of the piezoelectric elements 600 are formed an outer electrode 600a and an outer electrode 600b respectively. Each of the piezoelectric elements 600 is polarized, for example, in a direction shown by arrows xe2x80x9cPxe2x80x9d from the outer electrode 600a to the outer electrode 600b. (The direction in which the piezoelectric elements 600 are polarized may be reverse.)
The outer electrode 600b is directly and electrically connected to the vibrating plate 500 and is connected through the vibrating plate 500 serving as an electrode being common to each of the piezoelectric elements 600 to one pole of a driving power source 1000 of a pulse generator or a like.
Moreover, to the outer electrode 600a of each of the piezoelectric elements 600 is individually connected an electric signal line 601. Each of the piezoelectric elements 600 is connected through each of the electric signal lines 601 and each of ON/OFF controlling switch circuits 602 mounted to each of the piezoelectric elements 600 to the other pole of the driving power source 1000.
When a printing instruction is input, the ON/OFF controlling switch circuit 602 is turned ON and a voltage from the driving power source 1000 is applied to the piezoelectric elements 600. As a result, the piezoelectric elements 600 attempt to contract, by piezoelectric effects, in a direction of xe2x80x9cexe2x80x9d as shown in FIG. 9. However, in the piezoelectric elements 600, an amount of distortion in a face being bonded to the vibrating plate 500, since it is limited by a load of the vibrating plate 500, is made smaller than that in the face on a reverse side. Due to an asymmetry in the amount of distortion, the bonded portion between the piezoelectric elements 600 and the vibrating plate 500 is deformed in a manner to be extruded in a direction of xe2x80x9cfxe2x80x9d as shown in FIG. 9. This causes a volume in the pressure chamber 401 to decrease and ink existing in the pressure chamber 401 to be pressurized.
FIGS. 10A, 10B, and 10C are cross-sectional views showing configurations of FIG. 7 taken along a line Bxe2x80x94B to explain jetting operations of ink. FIG. 10A shows an initial state in which the ink pool 201, ink feeding port 301, pressure chamber 401, and nozzle 101 including its top end are filled with ink. When the ON/OFF controlling switch circuit 602 is turned ON in accordance with printing instruction, a voltage is produced in the piezoelectric element 600 and, as a result, the piezoelectric element 600 is deformed in a manner to be extruded in a direction xe2x80x9cgxe2x80x9d as shown in FIG. 10B. This causes ink in the pressure chamber 401 to be pressurized and the pressure in the pressure chamber 401 to be released to the nozzle 101 and the ink feeding port 301. As a result, ink is jetted on the nozzle 101. Then, when the ON/OFF controlling switch circuit 602 is turned OFF and electric charges in the piezoelectric element 600 are discharged, the piezoelectric element 600 is returned elastically to a direction xe2x80x9chxe2x80x9d as shown in FIG. 10C. By this movement, an amount of ink being equivalent to an amount that has flowed out from the pressure chamber 401 by the jetting of ink is fed from the ink pool 201 through the ink feeding port 301 to the pressure chamber 401 and the pressure chamber 401 is again filled with the ink and a series of operations is terminated. In actual operations, the series of operations is performed at high speed so that printing is done.
However, the ink jet type printer head having such the configurations as described above has a problem. That is, if the piezoelectric element 600 is to be bonded to the vibrating plate 500 after the vibrating plate 500 and pressure chamber plate 400 have been bonded to each other in assembling process, warp occurs at a place corresponding to a position of the pressure chamber 401 on the vibrating plate 500 by a load produced when the piezoelectric element 600 is bonded to the vibrating plate 500, failing to impose a proper load between the piezoelectric element 600 and the vibrating plate 500 and making it difficult to reduce thickness of the bonded portion.
Moreover, the thickness of the bonded portion is made non-uniform, thus causing a detrimental effect that dispersion in characteristics of expansion/contraction deformation in the piezoelectric element 600 and the vibrating plate 500.
As a means to solve inconvenience occurring when the assembling is performed in such orders as described above, a method is proposed in which the piezoelectric element 600 is bonded to the vibrating plate 500 in a manner that the load is imposed from the pressure chamber 401 side on a place corresponding to the position of the pressure chamber 401 on the vibrating plate 500. However, if this method is to be employed, there is a need for a system that can impose the load on the place corresponding to the position of the pressure chamber 401 on the vibrating plate 500 from the reverse side, thus causing complicated devices to be used for the assembling or bonding processes.
On the other hand, another method is proposed in which a load is uniformly imposed on a bonded portion between the piezoelectric element 600 and the vibrating plate 500 by first having bonded the piezoelectric element 600 to the vibrating plate 500 and then by fixing the vibrating plate 500 having the piezoelectric element 600 to the pressure chamber plate 400 by applying pressure and then by stacking them to finally form the printer head.
However, this method also has a following problem. That is, when the vibrating plate 500 with the piezoelectric element 600 bonded is to be fixed to the pressure chamber plate 400 by applying pressure, a part of the vibrating plate 500 can not be fixed properly on a surface of the pressure chamber plate 400. Because there is a groove-like clearance among the piezoelectric elements 600 existing on the vibrating plate 500.
A part of the vibrating plate 500 where the groove-like clearance is formed can not be fixed properly on a surface of the pressure chamber plate 400, more particularly, on an upper face of a partitioning wall section 402 among the pressure chambers 401, 401, . . . , simply by applying force to an upper face of the piezoelectric element 600 to push the vibrating plate 500 on the pressure chamber plate 400.
To solve this problem, a pressing jig 1100 as shown in FIGS. 11A and 11B is used. The pressing jig 1100 is so configured that a concave portion having a depth being slightly deeper than thickness of the piezoelectric element 600 is formed at a place corresponding to the piezoelectric element 600.
The vibrating plate 500, by fitting convex portions formed between the concave portions into the groove-like clearances among the piezoelectric elements 600 to directly press the vibrating plate 500, is fixed to an upper face of the partitioning wall section 402 among the pressure chambers 401, 401, . . . .
In order to use the pressing jig 1100 properly, high working accuracy of the pressing jig 1100 or alignment accuracy at a time of using it is required, thus causing a detrimental effect that the assembly process is made complicated. Moreover, since the thickness of the concave portion of the pressing jig 1100 is larger than that of the piezoelectric element 600, the pressure chamber plate 400 (that is, surface area except through hole of pressure chambers 401, 401 in the pressure chamber plate 400) cannot be fixed satisfactorily to the vibrating plate 500 at a place of an electrode taking-out section 600c mounted on the piezoelectric element 600, that is, at a part of the piezoelectric element 600 projecting outside of the pressure chamber 401, as shown in FIG. 11B, causing a likelihood of leak of ink from the bonded portion between the pressure chamber plate 400 and the vibrating plate 500 or peeling-off of the bonded portion.
Also, since a load on the piezoelectric element 600 imposed when the piezoelectric element 600 is individually separated by nachining is large, there is a high likelihood of the occurrence of burrs or cracks on the piezoelectric element 600. To solve these inconveniences, measures of making working speed lower and of making the piezoelectric element 600 thicker, and measures other than use of machining such a measure as disclosed in Japanese Patent Application Laid-open No. Hei 2-92644 in which a piezoelectric element is separated by an etching process are necessary, which present a big problem in production and commercialization.
Furthermore, such a method as disclosed in Japanese Patent Application Laid-open No. Hei 1-269546 is proposed in which a piezoelectric element is driven in a manner that a piezoelectric element is not separated individually and each of piezoelectric elements is operated independently for each electrode by printing an electrode pattern on a piece of the piezoelectric element. However, this method also presents a problem. That is, since each of the piezoelectric elements is integrated, which has the same thickness, the piezoelectric elements each being driven by a different electrode and existing in each of adjacent regions interfere with each other, causing an individual operation of each of the piezoelectric elements to be unstable, that is, causing jetting operations of ink in each of pressure chambers to be unstable.
In view of the above, it is an object of the present invention to provide an ink jet type printer head in which a pressure chamber plate, a vibrating plate, and a piezoelectric element can be properly stacked and bonded in its assembly without using a complicated pressing jig and in which the piezoelectric element can be properly operated for each of pressure chambers without interference.
According to a first aspect of the present invention, there is provided an ink jet type printer head including:
a plurality of pressure chambers each communicating with a nozzle and an ink pool;
a pressure chamber plate on which the plurality of pressure chambers are formed by boring holes;
piezoelectric elements which are fixed through a vibrating plate at places corresponding to the plurality of pressure chambers formed on the pressure chamber plate; and
wherein ink is jetted from the nozzle and ink is fed from the ink pool by changing a volume of each of the pressure chambers in accordance with expansion/contraction deformation of each of the piezoelectric elements and the vibrating plate and wherein grooves going around along corresponding positions inside a space section of each of the pressure chambers are formed on a surface of one piece of a piezoelectric element plate containing places corresponding to all the pressure chambers and a part of the piezoelectric element plate partitioned by the grooves acts as the piezoelectric element for each of the pressure chambers.
In the foregoing, a preferable mode is one wherein the grooves going around along inside portions of the space sections of the pressure chambers are provided by forming a plurality of straight-line like through-holes along positions corresponding to straight line sections and circular arc sections inside the space sections of the pressure chambers.
Also, a preferable mode is one wherein one piece of the piezoelectric element plate is made up of a sheet-like piezoelectric element main body and an outer electrode body covering a piezoelectric element main body and wherein the grooves penetrate at least the outer electrode bodies and are formed in a manner that cutting is performed up to the piezoelectric element main body.
Also, a preferable mode is one wherein the grooves are formed by an etching method.
Also, a preferable mode is one wherein the grooves are formed by a sandblasting method.
Also, a preferable mode is one wherein the grooves are formed by a dicing method.
Also, a preferable mode is one wherein the grooves are formed by a wire electric discharge machining method.
Furthermore, a preferable mode is one wherein a width of the groove accounts for 5% to 20% of that of the pressure chamber.
With the above configurations, the ink jet type printer head is so configured that the grooves going around along the corresponding position inside the space portion of each of the pressure chambers are formed on the surface of one piece of the piezoelectric element plate to partition the piezoelectric element plate and each portion of the piezoelectric element plate partitioned by these grooves acts as the piezoelectric element for each of the pressure chambers and, therefore, excessive clearance portions are not formed in a periphery of the piezoelectric element and simply by pressing the surface of the piezoelectric element in a stacking and assembling process of the piezoelectric element, vibrating plate, and pressure chamber plate, the vibrating plate can be fixed firmly not only to partitioning wall sections formed among the pressure chambers but also to the pressure chamber plate, thus solving problems of a leak of ink caused by defective bond and/or a peeling-off of members.
With another configuration, the piezoelectric elements are partitioned by the groove formed on the surface of the piezoelectric element plate and therefore an influence of adjacent piezoelectric elements on the piezoelectric element can be limited, thus enabling each of the piezoelectric element plates to be reliably operated as an independent piezoelectric element.
With another configuration, the grooves used to partition the piezoelectric element from other portions by going around the piezoelectric element plate and therefore not only ordinary groove working methods including etching and sandblasting but also working methods such as dicing or wire electric discharge machining in which forming of the groove at a specified portion with parts being left at both ends is impossible or the working method in which the change of forming direction of the groove in progress is impossible can be used, thus serving to improve the working accuracy and working speed and preventing the occurrence of burrs and cracks and enabling selection of the best suitable working method.
With another configuration, the piezoelectric element plate is made up of the sheet-like piezoelectric element main body and the outer electrode body covering the surface of the piezoelectric main body and therefore the separation of mechanical operations for each of the piezoelectric elements and the production of the outer electrode for each of the piezoelectric elements can be achieved simultaneously by simple groove working, thus allowing the manufacturing process to be simplified.